The invention relates generally to electric motors, and more specifically, to a technique for providing thermal and current control to an electric motor.
Rotating machines, such as electric motors, generators, and other similar devices, are quite common and may be found in diverse industrial, commercial, and consumer settings. These machines are produced in a variety of mechanical and electrical configurations. The configuration of these devices may depend upon the intended application, the operating environment, the available power source, or other similar factors. In general, these devices include a rotor surrounded at least partially by a stator.
For instance, one common design of electrical motor is the induction motor, which is used in numerous and diverse applications. Induction motors typically employ a stator assembly including a slotted core in which groups of coil windings are installed. By providing alternating current power to certain windings at certain times, a dynamic magnetic field is produced that causes the rotor to rotate within the stator. The rotational speed of the rotor is a function of the frequency of the alternating current power input and of the motor design (i.e. the number of poles defined by the windings). This rotation may be used to transmit a mechanical force to a driven load via an output shaft coupled between the rotor and the driven load.
Electric motors and other similar devices are generally configured to operate in a given temperature range. During operation, conventional motors typically generate heat. Indeed, physical interaction of the various moving components may produce heat by way of friction. Additionally, the electric current passing through the coil windings in the stator and rotor also produces heat, by way of resistive heating, for example. Similarly, electric motors and other similar devices are also intended to receive electrical current within a given range. If left unchecked, excessive heat or current may impair the performance of the motor. Worse yet, this excess heat or current may contribute to any number of malfunctions or system failure, which often leads to system downtime and required maintenance. Such events are undesirable because they impair productivity and lead to increased operating costs of such systems.
A number of devices are known in the art for protecting machines, such as electric motors, from excessive temperature or current. These control components include such devices as circuit breakers, fuses, switches, protective relays, thermal protectors, thermostats, and the like. Typically, these components are mounted on a wall, or in some enclosure, such as a motor control center, that is remote from the motor. While these devices may address some of the problems associated with excessive heat and current, the location of these devices remote from the motor can be problematic. In particular, remote placement of these devices does not allow for easy remote control of the motor. Further, such a location requires additional wiring when installing devices and longer downtime when a system malfunctions, resulting in significant installation and operating costs as well as lower productivity. In short, in most cases, such arrangements impose costs both of the additional components, wiring, enclosures, conduit and so forth, along with associated costs of installation.
There is a need, therefore, for an improved method for providing current and thermal protection to a rotating machine, such as an electric motor. There is a particular need for a method of protecting a motor in a fashion that requires less expense, while allowing for quicker repair and improved remote control of the motor.